INFLUENCE OP CERTAIN ELEMENTS ON STEEL. 391 by combustion. The strengthening eflect is 1140 Ib. for each 0.01 per cent, as determined by color, owing to the fact that the color-test does not determine all the carbon present. In basic steel each 0.01 per cent, of carbon strengthens steel by 770 Ib. per square inch when the carbon is determined by combustion. The strengthening effect is 820 Ib. for each 0.01 per cent, as determined by color. Phosphorus.—Each 0.01 per cent, of phosphorus strengthens steel by 1000 Ib. per square inch. Manganese.—Each 0.01 per cent, of manganese has a strengthening effect upon steel, and the effect is greater as the content of carbon increases. Below a certain content of manganese the effect is complicated by some disturbing condition, probably iron oxide, so that a decrease in manganese in very low-carbon steels is accompanied by an increase in strength. In acid steel each increase of 0.01 per cent, of manganese above 0.4 per cent, raises the strength of acid steel an amount varying from 80 Ib. in a metal containing 0.1 per cent, of carbon to 400 Ib. in a metal containing 0.4 per cent, of carbon. In basic steel each increase above 0.3 per cent, raises the strength an amount varying from 130 Ib. in a metal containing 0.1 per cent, of carbon to 250 Ib. in a metal containing 0.4 per cent, of carbon. Sulphur.—The effect of sulphur on the strength of acid and of basic steel is very small. Formula.—From the foregoing results, the following formulas may be written, in which 0=0.01 per cent, of carbon, P=0.01 per cent, of phosphorus, Mn=0.01 per cent, of manganese, E=a variable to allow for heat treatment, and the answer is the ultimate strength in pounds per square inch. The coefficient of manganese in acid steel, called x, is the value given in Table XYII-E, and applies only to contents above 0.4 per cent. The value of manganese in basic steel, called y, is the value given in T'able XVII-V, and applies to contents above 0.3 per cent. Formula for acid steel, carbon by combustion: 40,000+1000 0+1000 P+cc Mn+K=TJltimate Strength. Formula for basic steel, carbon by combustion: 41,500+770 0+1000 P+y Mn+E=Ultimate Strength.